Superconductor cables and magnetic devices

ABSTRACT

Superconducting cables and magnetic devices are disclosed.

INCORPORATION BY REFERENCE

[0001] The following documents are hereby incorporated by reference:U.S. Pat. No. 5,231,074, issued on Jul. 27, 1993, and entitled“Preparation of Highly Textured Oxide Superconducting Films from MODPrecursor Solutions,” U.S. Pat. No. 6,022,832, issued Feb. 8, 2000, andentitled “Low Vacuum Process for Producing Superconductor Articles withEpitaxial Layers,” U.S. Pat. No. 6,027,564, issued Feb. 22, 2000, andentitled “Low Vacuum Process for Producing Epitaxial Layers,” U.S. Pat.No. 6,190,752, issued Feb. 20, 2001, and entitled “Thin Films HavingRock-Salt-Like Structure Deposited on Amorphous Surfaces,’ PCTPublication No. WO 00/58530, published on Oct. 5, 2000, and entitled“Alloy Materials,” PCT Publication No. WO/58044, published on Oct. 5,2000, and entitled “Alloy Materials,” PCT Publication No. WO 99/17307,published on Apr. 8, 1999, and entitled “Substrates with ImprovedOxidation Resistance,” PCT Publication No. WO 99/16941, published onApr. 8, 1999, and entitled “Substrates for Superconductors,” PCTPublication No. WO 98/58415, published on Dec. 23, 1998, and entitled“Controlled Conversion of Metal Oxyfluorides into SuperconductingOxides,” commonly owned U.S. patent serial application Ser. No.09/616,860, filed on Jul. 14, 2000, and entitled “SuperconductorArticles and Compositions and Methods for Making Same,” commonly ownedU.S. patent serial application Ser. No. 09/615,991, filed on Jul. 14,2000, and entitled “Methods and Compositions for Making a Multi-layerArticle,” commonly owned U.S. patent application Ser. No. 09/618,811,filed on Jul. 14, 2000, and entitled “Methods of Making ASuperconductor,” commonly owned U.S. patent application Ser. No.09/694,400, filed on Oct. 23, 2000, and entitled “Precursor Solutionsand Methods of Using Same,” commonly owned U.S. patent application Ser.No. 09/500,717, filed on Feb. 9, 2000, and entitled “Coated ConductorThick Film Precursor,” commonly owned U.S. patent application Ser. No.09/616,566, filed on Jul. 14, 2000, and entitled “Control of Oxide LayerReaction Rates,” commonly owned U.S. patent application Ser. No.09/617,518, filed on Jul. 14, 2000, and entitled “Enhanced HighTemperature Coated Superconductors,” commonly owned U.S. patentapplication Ser. No. 09/617,520, filed on Jul. 14, 2000, and entitled“Enhanced Purity Oxide Layer Formation,” commonly owned U.S. patentapplication Ser. No. 09/615,669, filed on Jul. 14, 2000, and entitled“Oxide Layer Method,” commonly owned U.S. patent application Ser. No.09/615,999, filed on Jul. 14, 2000, and entitled “Multi-layer Articlesand Methods of Making Same,” commonly owned U.S. patent application Ser.No. 09/500,718, filed on Feb. 9, 2000, and entitled “Coated Conductorswith Reduced AC Loss,” commonly owned U.S. patent application Ser. No.09/855,312, filed on May 14, 2001, and entitled “Precursor Solutions andMethods of Using Same,” commonly owned U.S. patent application Ser. No.09/918,167, filed on Jul. 30, 2001, and entitled “Ion Texturing Methodsand Articles,” commonly owned U.S. Provisional Patent Application Ser.No. 60/305,478, filed Jul. 13, 2001, and entitled “Low StressSuperconductor,” and commonly owned U.S. Provisional Patent ApplicationSer. No. 60/308,957, filed on Jul. 31, 2001, and entitled“Superconductor Methods And Reactors.”

TECHNICAL FIELD

[0002] The invention relates to superconductor cables and magneticdevices.

BACKGROUND

[0003] Multi-layer superconductor articles, such as tapes, havingvarious architectures have been developed. Such articles often include asubstrate and a superconductor layer. Typically, one or more bufferlayers are disposed between the substrate and the superconductor layer.

SUMMARY

[0004] In general, the invention relates to superconductor cables andmagnetic devices.

[0005] In one aspect, the invention features an article that includes afirst layer formed of a first superconductor material and a second layerformed of a first electrically conductive material. The article alsoincludes a third layer formed of a second superconductor material and afourth layer formed of a second electrically conductive material. Thesecond layer is mechanically coupled to the first layer (e.g.,mechanically coupled at points other than their ends), and the fourthlayer is mechanically coupled to the third layer (e.g., mechanicallycoupled at points other than their ends). The second and fourth layersare in electrical communication. The first and second layers have aneutral mechanical axis when bent that is different than the neutralmechanical axis of the third and fourth layers when bent.

[0006] The phrase “mechanically coupled,” as used herein, refers to aforce between (e.g., at the interface of) two layers that substantiallyreduces (e.g., eliminates) the ability of one layer to moveindependently of the other layer. One example of mechanically coupledlayers is two layers that are chemically bonded together. Anotherexample of mechanically coupled layer is two layers that aremetallurgically bonded together. An additional example of mechanicallycoupled layers is two layers that are each adhered to an adhesive layertherebetween. It is to be noted that two layers (or other articles, suchas tapes) generally are not mechanically coupled when the layers (orarticles) are held in compression against each other by a force actingfrom outside (as opposed to at the interface of) the two layers. Forexample, if two tapes are wrapped within insulation that provides acompressive force that holds the tapes in proximity to each other, thisforce itself does not render the tapes mechanically coupled, althoughthe tapes may otherwise be mechanically coupled (e.g., if the tapes arechemically or metallurgically bonded to each other).

[0007] The article can be configured so that the second and fourthlayers can move independently of each other.

[0008] The first and second superconductor materials can be the same ordifferent. For example, one or both of the superconductor materials canbe a rare earth superconductor material, such as YBCO.

[0009] The first and second electrically conductive materials can be thesame or different. For example, the first and second electricallyconductive materials can be a metal (e.g., copper) or an alloy (e.g., acopper alloy).

[0010] The first and second layers can be in the form of a tape. Thesecond and third layers can be in the form of a tape.

[0011] The article can further include first and second substrates. Thefirst layer can be between the first substrate and the second layer, andthe third layer can be between the second substrate and the fourthlayer.

[0012] The article can further include first and second buffer layers.The first buffer layer can be between the first substrate and the firstlayer, and the second buffer layer can be between the second substrateand the third layer.

[0013] In some embodiments, the first substrate layer has a thicknessthat is about equal to a combined thickness of the first layer, thefirst buffer layer, and the second layer.

[0014] In certain embodiments, the fourth layer has a thickness that isabout equal to a combined thickness of the third layer, the secondbuffer layer, and the second substrate layer.

[0015] The article can further include first and second cap layers. Thefirst cap layer can be between the first and second layers, and thesecond cap layer can be between the third and fourth layers.

[0016] The article can further include an interfacial layer between thesecond and fourth layers. The interfacial layer is generally formed ofan electrically conductive material and can be, for example, capable ofreducing oxidation of the second and fourth layers, and/or reducingfriction between the second and the fourth layer. In some embodiments,the interfacial layer is at least partially formed or graphite.

[0017] In another aspect, the invention features an article (e.g., acable) that includes first and second helically wound superconductortapes. The first tape includes a superconductor layer and anelectrically conductive layer, and the second tape that includes asuperconductor layer and an electrically conductive layer. Theelectrically conductive layers of the first and second tapes are inelectrical communication (e.g., in electrical communication at more thanone position, such as by contacting each other in more than onelocation). The first helically wound superconductor tape has a neutralmechanical axis, and the second helically wound superconductor tape hasa different neutral mechanical axis.

[0018] The first and second helically wound tapes can be configured sothat they can move independently of each other.

[0019] The article can further include a forming element around whichthe first and second tapes are helically wound.

[0020] In some embodiments, the superconductor layers of the firstand/or second superconductor tapes are mechanically compressed.

[0021] The first and second helically wound superconductor tapes canhave a common helical axis.

[0022] In some embodiments, the article further includes third andfourth helically wound superconductor tapes. The third helically woundsuperconductor tape includes a superconductor layer and an electricallyconductive layer, and the fourth helically wound superconductor tapeincludes a superconductor layer and an electrically conductive layer.The electrically conductive layers of the third and fourthsuperconductor tapes have more than one point of electricalcommunication (e.g., by contacting each other in more than onelocation). The third and fourth helically wound superconductor tapes canhave a common helical axis.

[0023] In certain embodiments, the electrically conductive layers of thefirst and second superconductor tapes at least partially overlap. Insome embodiments, the electrically conductive layers of the first andsecond superconductor tapes substantially entirely overlap.

[0024] In a further aspect, the invention features an article thatincludes first and second pluralities of helically wound tapes. In thefirst plurality of helically wound superconductor tapes, each tapeincludes a layer of a superconductor material and a layer of anelectrically conductive material, and each tape is wound in parallel ina first direction. In the second plurality of helically woundsuperconductor tapes, each tape includes a layer of a superconductormaterial and a layer of an electrically conductive material, and eachtape is wound in parallel in a second direction opposite the firstdirection. The layer of the electrically conductive materials in eachtape in the first plurality of tapes has more than one position ofelectrical communication with the layer of electrically conductivematerial in each tape of the second plurality of tapes (e.g., bycontacting each other in more than one location).

[0025] In some embodiments, the first and second pluralities ofhelically wound superconductor tapes have a common helical axis.

[0026] In certain embodiments, the electrically conductive layers ofeach tape in the first plurality of superconductor tapes at leastpartially overlap with the electrically conductive layers of each tapein the second plurality of superconductor tapes.

[0027] Each of the tapes in the article can have a different neutralmechanical axis when bent than the neutral mechanical axis of any of theother tapes when bent.

[0028] In an additional aspect, the invention features a superconductingmagnetic coil that includes first and second coiled superconductortapes. Each coiled superconductor tape is coiled about a respective coilaxis. The first coiled superconductor tape includes a superconductorlayer and an electrically conductive layer. The electrically conductivelayer of the first coiled superconductor tape has a surface that formsan inner surface of the first coiled superconductor tape. The innersurface of the first coiled superconductor tape faces the coil axis ofthe first coiled superconductor tape. The second coiled superconductorincludes a superconductor layer and an electrically conductive layer.The electrically conductive layer of the second coiled superconductortape has a surface that forms an outer surface of the second coiledsuperconductor tape. The outer surface of the second coiledsuperconductor tape faces away from the coil axis of the second coiledsuperconductor tape. The first and second coiled superconductor tapesare configured so that inner surface of the first superconductor tape isadjacent the outer surface of the second superconductor tape.

[0029] The first and second superconductor tapes in the magnetic coilcan have different neutral mechanical axes from each other.

[0030] In some embodiments, the first and second coiled superconductortapes contact each other.

[0031] In certain embodiments, the first and second coiledsuperconductor tapes are wound together.

[0032] In some embodiments, the coil axis of the first superconductortape is the same as the coil axis of the second superconductor tape.

[0033] In certain embodiments, the first and second superconductor tapesare coiled about each other.

[0034] In some embodiments, the superconductor layer and electricallyconductive layer of the first superconductor tape are mechanicallycoupled (e.g., mechanically coupled at points other than their ends),and the superconductor layer and electrically conductive layer of thesecond superconductor tape are mechanically coupled (e.g., mechanicallycoupled at points other than their ends).

[0035] In certain embodiments, the superconductor layers of the firstand/or second superconductor tapes are mechanically compressed.

[0036] The superconducting magnetic coil can further include aninterfacial layer disposed between the adjacent first and secondsuperconductor tapes.

[0037] The superconducting magnetic coil can further include third andfourth coiled superconductor tapes. Each of the third and fourth coiledsuperconductor tapes is coiled about a respective coil axis. The thirdcoiled superconductor tape includes a superconductor layer and anelectrically conductive layer. The electrically conductive layer of thethird coiled superconductor tape has a surface that forms an innersurface of the third coiled superconductor tape. The inner surface ofthe third coiled superconductor tape faces the coil axis of the thirdcoiled superconductor tape. The fourth coiled superconductor includes asuperconductor layer and an electrically conductive layer. Theelectrically conductive layer of the fourth coiled superconductor tapehas a surface that forms an outer surface of the fourth coiledsuperconductor tape. The outer surface of the fourth coiledsuperconductor tape faces away from the coil axis of the fourth coiledsuperconductor tape. The third and fourth coiled superconductor tapesare configured so that inner surface of the third superconductor tape isadjacent the outer surface of the fourth superconductor tape.

[0038] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can allow multiple superconductor layersto simultaneously be compressed (e.g., by being at or below the neutralmechanical axis) when the articles are bent.

[0039] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can reduce the risk of reduced currentdensity due to, for example, the presence of defects (e.g., localizeddefects, such as a crack a grain boundary, or the like) in one or moreof the superconductor layers.

[0040] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can result in current sharing through, forexample, redundant conducting paths, lower hysteretic losses underalternating current conditions, enhanced electrical stability, and/orenhanced thermal stability.

[0041] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can result in a favorable stress profileand/or improved mechanical properties.

[0042] The architecture of the superconductor articles (e.g., tapes,cables, and/or magnetic coils) can provide improved mechanicalstability, improved electrical stability, enhanced current carryingcapacity, and/or favorable economy of manufacture.

[0043] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can reduce mechanical degradation of theoperational superconductor layer(s) during bending.

[0044] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can make it relatively easy to splice thearticles.

[0045] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can make it relatively easy to achievetermination of tape stack ups and/or conductor elements.

[0046] The architecture of the superconductor articles (e.g., tapes,cables and/or magnetic coils) can reduce heating due to, for example,localized defects in the superconductor material.

[0047] The superconductor articles (e.g., tapes, cables and/or magneticcoils) can be used in a variety of applications, including, for example,electrical, magnetic, electro-optic, dielectric, thermal, mechanical,and/or environmental (e.g., protective) applications.

[0048] Other features, objects, and advantages of the invention will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0049] FIG. 1 is a cross-sectional view of an embodiment of asuperconductor article including two superconductor tapes;

[0050] FIG. 2 is a cross-sectional view of an embodiment of thesuperconductor article of FIG. 1 when bent;

[0051] FIG. 3 is a plan view of an embodiment of a superconductor tape;

[0052] FIG. 4 is a cross-sectional view of the superconductor tape ofFIG. 3;

[0053] FIG. 5A is a plan view of an embodiment of a superconductor tape;

[0054] FIG. 5B is a plan view of an embodiment of a superconductor tape;

[0055] FIG. 6 is a cross-sectional view of an embodiment of asuperconductor tape; and

[0056] FIGS. 7A and 7B are perspective and plan views, respectively, ofan embodiment of a superconductor magnetic coil.

[0057] Like reference symbols in the various drawings indicate likeelements.

DETAILED DESCRIPTION

[0058] FIG. 1 shows a cross-sectional view of an embodiment of asuperconductor article 1000 that includes multi-layer superconductortapes 1100 and 1200. Tape 1100 includes a substrate 1110, a buffer layer1120, a superconductor layer 1130, and an electrically conductingstabilizer layer 1140. Similarly, tape 1200 includes a substrate 1210, abuffer layer 1220, a superconductor layer 1230, and an electricallyconducting stabilizer layer 1240. The layers within tapes 1100 and 1200are mechanically coupled (e.g., chemically bonded or metallurgicallybonded) to their corresponding neighboring layers (e.g., mechanicallycoupled at points other than their ends), but tapes 1100 and 1200 areconfigured so that they can move independently of each other because,while stabilizer layers 1140 and 1240 contact each other and are inelectrical communication, surface 440 of stabilizer layer 1140 is notmechanically coupled (e.g., is not chemically bonded or metallurgicallybonded) to surface 470 of stabilizer layer 1240.

[0059] With the architecture of article 1000, electrical current canreadily propagate along and between tapes 1100 and 1200, even if alocalized defect is present in superconductor layers 1130 and/or 1230.For example, in the case that a localized defect (e.g., a crack, a grainboundary, or the like) is present in superconductor layer 1130,electrical current in the vicinity of the defect can be shunted throughstabilizer layers 1140 and 1240 and into superconductor layer 1230.Likewise, if a localized defect is present in superconductor layer 1230,electrical current in the vicinity of the defect can be shunted throughstabilizer layers 1240 and 1140 and into superconductor layer 1130. Thiscan enhance both the electrical stability and/or the current carryingcapacity of article 1000 compared to certain other superconductorarticles in which the superconductor layers in neighboring tapes are notin electrical communication with each other.

[0060] Moreover, the architecture of article 1000 can provide enhancedelectrical stability and/or enhanced current carrying capacity even inthe absence of localized defects in one of superconductor layers 1130and/or 1230 because these layers are in electrical communication witheach other via stabilizer layers 1140 and 1240, thereby increasing thevolume of electrically conductive (including superconductive) materialin electrical communication in article 1000 relative to other systems inwhich the superconductor layers of neighboring tapes are not inelectrical communication with each other.

[0061] In addition, by allowing tapes 1100 and 1200 to moveindependently of each of other, tapes 1100 and 1200 can be designed sothat, when exposed to certain conditions of stress (e.g., when bent,such as when formed in a cable or a magnetic coil), they each have theirown neutral mechanical axis (i.e., lowest strain region). This is shown,for example, in FIG. 2 where tapes 1100 and 1200 are bent. Tape 1100 hasa neutral mechanical axis 1150, and tape 1200 has a neutral mechanicalaxis 1250. Without wishing to be bound by theory, it is believed thatsuperconductor layers 1130 and 1230 have a higher critical currentdensity when compressed than when expanded. Because tapes 1100 and 1200have independent neutral mechanical axes, tapes 1100 and 1200 can bedesigned so that, when bent, superconductor layers 1130 and 1230 arelocated at or below neutral mechanical axes 1150 and 1250, respectively.This allows superconductor layers 1130 and 1230 to simultaneously be ina compressed state when tapes 1100 and 1200 are bent.

[0062] In some embodiments, the distance the superconductor layer isfrom the neutral mechanical axis is less than about 10 percent (e.g.,less than about nine percent, less than about eight percent, less thanabout seven percent, less than about six percent, less than about fivepercent, less than about four percent, less than about three percent,less than about two percent, less than about one percent) of thethickness of the tape.

[0063] In certain embodiments, the thickness of the layers in tapes 1100and/or 1200 can be selected so that, when tapes 1100 and/or 1200 arebent, superconductor layers 1130 and/or 1230, respectively, are at orbelow neutral mechanical axes 1150 and/or 1250, respectively. As anexample, in some embodiments, the thickness of substrate 1110 is aboutthe same as or greater than the combined thickness of the of stabilizerlayer 1140, superconductor layer 1130 and buffer layer 1120. Forexample, the thickness of substrate 1110 can be at least about onepercent greater (e.g., at least about two percent greater, at leastabout three percent greater, at least about four percent greater, atleast about five percent greater, at least about eight percent greater,at least about 10 percent greater) than the combined thickness layers1140, 1130 and 1120. As another example, in certain embodiments, thethickness of stabilizer layer 1240 is about the same as or greater thanthe combined thickness of the of substrate 1210, buffer layer 1220, andsuperconductor layer 1230. For example, the thickness of layer 1240 canbe at least about one percent greater (e.g., at least about two percentgreater, at least about three percent greater, at least about fourpercent greater, at least about five percent greater, at least abouteight percent greater, at least about 10 percent greater) than thecombined thickness layers 1210, 1220 and 1230.

[0064] In some embodiments, layer 1110 is from about 20 microns to about80 microns thick (e.g., from about 30 microns to about 70 microns thick,from about 40 microns to about 60 microns thick, about 50 micronsthick).

[0065] In certain embodiments, layer 1120 is from about 0.1 micron toabout 0.5 micron thick (e.g., from about 0.2 micron to about 0.4 micronthick, about 0.3 micron thick).

[0066] In some embodiments, layer 1130 is from about 0.7 micron to about1.3 microns thick (e.g., from about 0.8 micron to about 1.2 micronsthick, from about 0.9 micron to about 1.1 microns thick, about onemicron thick).

[0067] In certain embodiments, layer 1140 is from about 45 microns toabout 51 microns thick (e.g., from about 46 microns to about 50 micronsthick, from about 47 microns to about 49 microns thick, about 48.7microns thick).

[0068] In some embodiments, layer 1210 is from about 20 microns to about80 microns thick (e.g., from about 30 microns to about 70 microns thick,from about 40 microns to about 60 microns thick, about 50 micronsthick).

[0069] In certain embodiments, layer 1220 is from about 0.1 micron toabout 0.5 micron thick (e.g., from about 0.2 micron to about 0.4 micronthick, about 0.3 micron thick).

[0070] In some embodiments, layer 1230 is from about 0.7 micron to about1.3 microns thick (e.g., from about 0.8 micron to about 1.2 micronsthick, from about 0.9 micron to about 1.1 microns thick, about onemicron thick).

[0071] In certain embodiments, layer 1240 is from about 48 microns toabout 53 microns thick (e.g., from about 49 microns to about 52 micronsthick, from about 50 microns to about 52 microns thick, about 51.3microns thick).

[0072] Substrates 1110 and 1210 are typically formed of conventionalsubstrate materials. Such materials include, for example, metals andalloys, such as nickel, silver, copper, zinc, aluminum, iron, chromium,vanadium, palladium, molybdenum or their alloys.

[0073] Buffer layers 1120 and 1220 are generally formed of conventionalbuffer layer materials. Examples of such materials include metals, metaloxides and/or metal oxides, such as silver, nickel, CeO₂, Y₂O₃, TbOx,GaOx, yttria stabilized zirconia (YSZ), LaAlO₃, SrTiO₃, Gd₂O₃, LaNiO₃,LaCuO₃, SrTuO₃, NdGaO₃, NdAlO₃, MgO, AlN, NbN, TiN, VN and ZrN.

[0074] In general, superconductor layers 1130 and 1240 are formed ofrare earth oxide superconductor materials. Examples of such materialsinclude rare earth copper oxide superconductors, such as rare earthbarium copper oxides (e.g., YBCO, GdBCO and ErBCO).

[0075] Typically, the substrate/buffer layer/superconductor layerarrangement in tapes 1100 and 1200 is formed via epitaxial growth.Accordingly, surfaces 432, 434 and 436 of substrate 1110, buffer layer1120 and superconductor layer 1130, respectively, are usually textured(e.g., biaxially textured or cube textured). Similarly, surfaces 484,482 and 470 of substrate 1210, buffer layer 1220 and superconductorlayer 1230, respectively, are usually textured (e.g., biaxially texturedor cube textured).

[0076] Stabilizer layers 1140 and 1240 are generally formed ofelectrically conductive materials, such as metals and/or alloys.Examples of materials from which layers 1140 and 1240 can be formedinclude copper, nickel, silver and alloys thereof.

[0077] Generally, a tape has a length dimension that is substantiallygreater than its width or breadth. Exemplary dimensions are micrometersto hundreds of micrometers in height (e.g., at least one micrometer, atleast two micrometers, at least five micrometers, at least 10micrometers, at least 20 micrometers, at least 50 micrometers, at least100 micrometers, at least 200 micrometers, at least 1000 micrometers),millimeters to centimeters in width (e.g., at least one millimeter, atleast two millimeters, at least five millimeters, at least 10millimeters, at least 20 millimeters), and fractions of a meter tothousands of meters in length (e.g., at least 0.01 meter, at least 0.2meters, at least 0.1 meters, at least 1 meter, at least 10 meters, atleast 100 meters).

[0078] In some embodiments, superconductor tapes 1100 and 1200 can beincluded in superconductor cables. FIGS. 3 and 4 show plan andcross-sectional views, respectively, of a portion of an embodiment of asuperconductor cable 400 in which a layer 404 of cable 400 is formedfrom superconductor tape 1100 and a layer 406 of cable 400 is formedfrom superconductor tape 1200. Tapes 1100 and 1200 are configured tomove relatively independent of each other (e.g., they are notmechanically coupled to each other). Tape 1100 is helically wound arounda helical axis 420 so that surface 430 of tape 1100 faces toward helicalaxis 420 and surface 440 of tape 1100 faces away from helical axis 420.The helix formed by tape 1100 has a helical pitch 450, which correspondsto the distance along helical axis 420 in which tape 1100 is woundthrough 360°. Generally, pitch 450 can be varied as desired. As anexample, pitch 450 can be about equal to the width of tape 1100 so thatalternate windings of tape 1100 are adjacent each other. As anotherexample, pitch 450 can be much longer or shorter than the width of tape1100.

[0079] Tape 1200 is helically wound over the tape 1100 and aroundhelical axis 420 in the opposite direction to tape 1100. Tape 1200 iswound with surface 470 facing toward helical axis 420 and surface 480facing away from helical axis 420. Tape 1200 has a helical pitch 490which can generally be varied as desired. As an example, helical pitch490 can be about equal to the width of tape 1200 so that alternatewindings of tape 1200 are adjacent each other. Helical pitch 490 can beabout the same as, shorter than, or longer than helical pitch 450.

[0080] Surface 470 of tape 1200 contacts surface 440 of tape 1100periodically along the cable at points 499. Points 499 typically arepoints of electrical communication between tapes 1100 and 1200, allowingelectrical current to pass between tapes 1100 and 1200 via stabilizerlayers 1140 and 1240.

[0081] Referring to FIG. 4, cable 400 can be formed by winding tapes1100 and 1200 around a forming element 401. Optionally, forming element401 can be removed after winding, or can remain as a structuralcomponent of cable 400. Optionally or additionally, forming element 401can be used to supply a cryogenic fluid to cable 400 in order to cooltapes 1100 and/or 1200 (e.g., to a temperature that is about the same asor below the critical temperature of superconductor layers 1130 and/or1230).

[0082] While embodiments have been described in which each layer of asuperconductor tape is formed by a helically winding a single tapearound a helical axis in a given direction, the invention is not solimited.

[0083] As an example, more than one (e.g., two, three, four, five, six,seven, eight, etc.) superconductor tapes can be helically wound besideeach other in the same direction around a helical axis to form a layerof a superconductor tape. FIG. 5A is a plan view of an embodiment of alayer of a cable 500 that includes two superconductor tapes 1100a and1100b that are helically wound beside each other about a helical axis520 in the same direction. FIG. 5B is a plan view of an embodiment of asuperconductor cable 800, including four tapes 810, 820, 830, and 840.Two tapes, 810 and 820, are wound in a first helical direction around aforming element 801. Tape 810 and tape 820 are wound parallel. Twoadditional tapes, 830 and 840, are wound in a second helical direction,opposite the first helical direction, around forming element 801 on topof tapes 810 and 820. Tapes 830 and 840 are wound parallel. The numberof superconductor tapes helically wound beside each other in each layerof a superconductor cable can be the same as or different than thenumber of superconductor tapes helically wound beside each other in theother layers of the superconductor cable. In some embodiments, one layerof a superconductor cable may be formed of a single tape while one ormore other layers of the superconductor cable may be formed of multipletapes wound beside each other.

[0084] As another example, more than one (e.g., two, three, four, five,six, seven, eight, etc.) superconductor tapes can be stacked on top ofeach other and then helically wound around a helical axis in the samedirection to form a layer of a superconductor tape. In such embodimentsthe superconductor tapes are stacked so that the tapes form pairs inwhich the stabilizer layers contact each other. FIG. 6 shows anembodiment of a layer of a cable 600 that is formed of twosuperconductor tapes 1100 and 1200 that are stacked on each other andhelically wound around a helical axis 620 in the same direction. Thenumber of superconductor tapes stacked on each other in each layer ofsuperconductor cable 600 can be the same as or different than the numberof superconductor tapes that are stacked on each other in the otherlayers of cable 600. Optionally, a layer of electrically insulatingmaterial can be wound positioned between tapes 1100 and 1200.

[0085] In some embodiments, cables having sufficient current transferterminations can be relatively easily fabricated and the overall currentdensity of the cable can be relatively high. As an example, the currentdensity can be greater than about 6000 Amperes.

[0086] In certain embodiments, one or more of the tapes in asuperconductor cable can have an electrically conductive stabilizerlayer with a free surface, and the tape layers can be separated at thecable ends to expose the free surfaces. In some embodiments, one or moreof the exposed free surface of the stabilizer layer(s) can be used as aterminal for current transfer into and/or out of the superconductortape.

[0087] While the superconductor tapes described herein have beendiscussed with respect to their use in superconductor cables, thesuperconductor tapes can also be used in other applications, such as,for example, superconductor coils (e.g, magnetic coils). FIGS. 7A and 7Bshow perspective and plan views, respectively, of a superconductor coil600 including multiple turns (710, 715, 720, 725, etc.) wound aroundcoil axis 630 with each turn formed by superconductor tapes 1100 and1200. Tapes 1100 and 1200 are generally not mechanically coupled, butmay be mechanically coupled at their respective ends. In each turn ofcoil 600, surface 440 of tape 1100 contacts surface 470 of tape 1200 sothat tapes 1100 and 1200 are in electrical communication. In addition,in adjacent turns of coil 600, surface 430 of tape 1100 contacts surface480 of tape 1200 in the adjacent turn. In some embodiments, one or morematerials (e.g., an electrically insulating material, such as anelectrically insulating cloth) may be coiled between adjacent turns(e.g., between surfaces 430 and 480 of adjacent turns).

[0088] While embodiments of a superconductor coil having each turnformed of one superconductor tape pair have been described, theinvention is not so limited. In general, a superconductor coil can haveeach turn formed of any desired number of superconductor tape pairs(e.g., two tape pairs, four tape pairs, six tape pairs, eight tapepairs, etc.). Typically, each tape pair within a turn is configured sothat the stabilizer layers contact each other, so that the tapes withineach tape pair are in electrical communication, and so that thesubstrates of adjacent tape pairs contact each other.

[0089] While the foregoing description has been with respect tosuperconductor tapes that include certain layers (substrate, bufferlayer, superconductor layer, and stabilizer layer), the invention is notlimited in this sense. A superconductor tape can include additionallayers. In these embodiments, the layers are preferably arranged so thatthe superconductor layer(s) are below the neutral mechanical axis of thetape. In some embodiments, this can be achieved by using a stabilizerhaving a thickness that is about the same or greater than the combinedthickness of the other layers in the tape. In certain embodiments, thiscan be achieved by using a substrate having a thickness that is aboutthe same or greater than the combined thickness of the other layers inthe tape.

[0090] In some embodiments, a superconductor tape can include more thanone buffer layer (e.g., two buffer layers, three buffer layers, fourbuffer layers, etc.). The multiple buffer layers can be stacked on topof each other. In certain embodiments, a superconductor tape can includemore than one superconductor layer. The multiple superconductor layerscan be stacked on top of each other. A superconductor tape can includeintercalated buffer layers and superconductor layers.

[0091] In some embodiments, a superconductor tape can include a caplayer between the superconductor layer and the stabilizer layer. The caplayer can, for example, be formed of an electrically conductive materialthat is less reactive with the superconductor material than the materialfrom which the stabilizer layer is formed. Examples of material fromwhich the solder can be formed include silver, gold, palladium andplatinum.

[0092] In certain embodiments, a superconductor tape can include asolder layer between the cap layer and the stabilizer layer. The solderlayer can, for example, assist in adhesion between the cap andstabilizer layers. Examples of materials from which the solder layer canbe formed include certain lead-tin based solders (e.g., a soldercontaining about 62% lead, about 36% tin and about two percent silver,or a solder containing about 95% lead about five percent tin). Otherappropriate solders are known to those skilled in the art.

[0093] In addition, while superconductor articles have been described inwhich the stabilizer layers of adjacent tapes are in contact, otherembodiments are also possible. More generally, the stabilizer layersneed not be in contact, but are preferably in electrical communicationand arranged so that each tape has its own neutral mechanical axis. Forexample, a layer of material, such as a layer of an electricallyconductive material that reduces friction between the adjacentstabilizer layers and/or a layer of an electrically conductive materialthat reduces oxidation of one or both of the adjacent stabilizer layers,can be located between the adjacent stabilizer layers. In someembodiments, a layer of graphite can be positioned between adjacentstabilizer layers. In certain embodiments, molybdenum disulfide can bepositioned between adjacent stabilizer layers. In some embodiments, oneor more adjacent stabilizer layers can contain (e.g., be impregnatedwith) an appropriate lubricant material, such as one or more greases(e.g., one or more electrically conductive greases). In certainembodiments, a hard layer (e.g., a thin, hard layer) of material (e.g.,electrically conductive material, such as chrome, nickel and/or certainnitride materials) can be disposed between adjacent stabilizers (e.g.,formed as an additional layer on top of one or both stabilizer layers).

[0094] In certain embodiments (e.g., when a tape is configured so thatthe stabilizer layer is facing the helical axis), the thickness of theis stabilizer is about the same or greater than the combined thicknessof the substrate, buffer and superconductor layers. In some embodiments(e.g., when a tape is configured so that the stabilizer layer is facingaway from the helical axis), the thickness of the is stabilizer is aboutthe same or less than the thickness of the substrate less the thicknessof the buffer layers less the thickness of the superconductor layers.

[0095] In general, when two layers are mechanically coupled, they can bemechanically coupled at points other than their ends. As an example,they can be mechanically coupled along the entire surfaces of contact.As another example, they can be intermittently mechanically coupled atpoints along their surfaces.

[0096] Other embodiments are in the claims.

1. An article comprising: a first layer comprising a firstsuperconductor material; a second layer comprising a first electricallyconductive material, the second layer being mechanically coupled to thefirst layer so that, when bent, the first and second layers have a firstneutral mechanical axis; a third layer comprising a secondsuperconductor material; and a fourth layer comprising a secondelectrically conductive material mechanically coupled to the thirdlayer, so that, when bent, the third and fourth layers have a secondneutral mechanical axis different than the first neutral mechanicalaxis, wherein the second and fourth layers are in electricalcommunication. 2-57. (cancelled)